PumpTech Customer EducationPumpTech Customer Education

Bellevue Moses Lake Canby

http://www.Pumptechnw.com

Pump Ed 101

Joe Evans, Ph.D http://www.PumpEd101.com

http://www.Pump-Zone.com

Two Steps to Longer Pump & Motor Life

The Primary Cause of Pump Failure

What is the primary cause of pump failure?

Answer: The system in which it operates.

What composes the system?

Answer: Hydraulic, Electrical, & Mechanical

4Pump Ed 101

The Two Most Important Preventive Maintenance Steps

Determine the “as built”, pump operating point on the head / capacity curve and correct if necessary.

Measure the voltage unbalance and correct if necessary.

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The Performance Curve

BEBOP

Pump Ed 101

System Hydraulics –

Radial Thrust

Ideally a pump should operate between 90% and 110% of its BEBOP.

If it does not, the radial forces that act upon a centrifugal pump’s impeller can account for a large percentage of premature failures.

The resulting shaft deflection will decrease mechanical seal, wear ring, and bearing life.

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•

Forms about the periphery of the impeller due to uneven volute geometry

•

A function of total head and and width and diameter of the impeller

•

Usually reaches a maximum at or near shut off head

Radial Thrust

Pump Ed 101

Radial Thrust versus % BEP Flow

Radial Thrust

0

20

40

60

80

100

120

0 20 40 60 80 100 120 140 160 180 200

Percent BEP Flow

Perc

ent R

adia

l Thr

ust

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Reliability versus % BEP Flow

Reliability

0

20

40

60

80

100

120

0 20 40 60 80 100 120 140 160

Percent BEP Flow

Rel

iabi

lity

Fact

or

11

API

Pump Ed 101

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Realiability Versus Radial Thrust

0

20

40

60

80

100

120

0 20 40 60 80 100 120 140 160 180

Percent BEP Flow

% T

hrus

t & R

elia

bilit

y

ReliabilityRadial Thrust

Reliability versus Radial ThrustReliability versus Radial Thrust

Pump Ed 101

Pump ED 101

Radial Thrust Calculation

FR = KR x (H x s/2.31) x D2 x b2

FR = Radial Thrust in Pound FeetKR = Thrust FactorH = Head per stage in Feets = Specific GravityD2 = Impeller Diameter in Inchesb2 = Impeller Width at Discharge in Inches

Radial Thrust Example

FR

= KR

x (H x s/2.31) x D2

x b2

11.9”

X 3.5”

Impeller Ns = 1785

100% BEBOP

KR = 0.03H = 110’s = 1D2 = 11.9”b2 = 3.5”FR = 59 lb

40% BEBOP

KR = 0.21H = 138’s = 1D2 = 11.9”b2 = 3.5”FR = 522 lb

Pump Ed 101

System Hydraulics -

RecirculationThree types of recirculation can occur when a pump is operated to the left side of the performance curve.Normal recirculation increases with wear ring clearance & reduced flow.Suction & Discharge recirculation increase as flow is reduced.The resulting recirculation cavitation will cause internal damage over time.

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Recirculation Cavitation

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Discharge Recirculation Cavitation

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Occurs on the high pressure side of the vane

Eye Diameter Effect on NPSHr

Pump Ed 101

Suction Recirculation Cavitation

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Occurs on the high pressure side of the vane

Determine The Pump Operating Point

Pump Down Application Example

Measure flow with a flow meterorMeasure the time required to remove one foot of water.Measure discharge head with a gauge

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Time Required To Pump Down One Foot

Calculate the volume per basin foot(cubic feet X 7.48)

Measure distance to “pump on”

level

Start pump and record time to pumpdown one foot

Example: 10ft diameter wet well

Volume = 3.14 X 52

x 1 = 78.5 ft3

Volume = 78.5 x 7.48 = 587 gal/ftPumping Time = 58 secAve Flow = 600 gpm

Pump On Level

Pump Ed 101

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NonNon--clogclog PumpPump

Measuring Total Pump Head With A Gauge

Start the pump at the “pump on”

level

Measure pressure and convertto feet by multiplying by 2.31

Add the vertical distance from the gauge to the water level in the wet well to obtain total pump head

Example: 24psi X 2.31 = 55’55’

+ 10’

= 65’

TDH

Pump Ed 101

As Built Operating Point (H4H –

10”

Trim)

23

600 GPM @ 65’

Pump Ed 101

As Built Performance –

Fixes

If flow is too far to the right of BEP, trim the impeller or reduce maximum speed if the pump is under VFD control. Lower the pump start level.

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If flow is too far to the left of BEPCheck for restrictions or blockage in the systemRaise the pump start levelInstall larger impeller if HP is adequateReplace the pump

Pump Ed 101

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Electrical System

Pump Ed 101

Unbalanced Phase Voltage

Unbalanced phase voltage is the most common electrical problem found in pump installations.

A small percentage of voltage unbalance can result in a much larger current unbalance.

Unbalanced current increases the operating temperature and reduces stator life.

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Unbalanced Phase VoltageUnbalanced Phase Voltage

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Unbalanced Phase Voltage

Insulation LifeInsulation Life

Pump ED 101

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% voltage unbalance

Winding temp.

(°C)

I2R losses

(% of total)

Efficiency reduction

Expected winding life

(years)

0 120 30% — 20 1 130 33% Up to 1/2% 10 2 140 35% 1-2% 5 3 150 38% 2-3% 2.5 4 160 40% 3-4% 1.25 5 180 45% 5% or more Less than 1

Pump Ed 101

Unbalanced Phase VoltageUnbalanced Phase Voltage Effect on Winding Temperature & Motor Life (DOE)Effect on Winding Temperature & Motor Life (DOE)

Measuring Voltage Unbalance

Measure L1/L2, L2/L3, L3/L1 voltages (pump on & off)

Add together and divide by 3 (average voltage)Determine the greatest variation from the average%Unbalance = 100 X (variation / average)For every 1% of voltage unbalance you can expect 5 – 8% of current unbalance

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Voltage Unbalance -

Example

L1/L2 = 462 L2/L3 = 465 L3/L1 = 447

462 + 465 + 447 = 1374

1374 / 3 = 458

Largest variation from average: 458 – 447 = 11

%Unbalance = 100 X (11/458) = 2.4%

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Voltage Unbalance –

Fixes

If voltage unbalance is greater than 1% with the motor off, contact your utility

If voltage unbalance is greater than 1% with the motor running, roll the motor leads

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Voltage Unbalance –

Rolling the Leads

Step 1 - on the motor side of the contactor move M1 to M2, M2 to M3, and M3 to M1

Step 2 - start the motor and measure voltage unbalance

Step 3 - Repeat step 1 by moving M1 to M3, M2 to M1 and M3 to M2

Step 4 - repeat Step 2

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Voltage Unbalance –

Rolling the Leads

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L1 L2 L3

M1 M2 M3M3 M1 M2M2 M3 M1

Pump Ed 101

Voltage Unbalance –

Rolling the Leads

If the voltage unbalance is 1% or less with one of the alternative connections, use that connection.

If unbalance cannot be corrected by rolling the leads, its source must be located and corrected.

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Voltage Unbalance Locating the Source

If the leg with the most imbalance stays with the same incoming power lead, the power source is the problem.

If the leg with the most imbalance moves with the motor lead, the motor side is the problem.

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Voltage Unbalance Causes & Fixes

Power Side –

worn or corroded contactor, inconsistent conductor size, unbalanced single phase loads, single phase ground faults, line voltage regulator settings, power factor correction capacitors, harmonic distortion from non-linear loads (multimeter?), 120 hz vibration, VFD

39

Motor Side –

damaged cable, bad splice, poor connections, faulty motor winding

Pump Ed 101

Pump Ed 101

Joe Evans, Ph.D http://www.PumpEd101.com

http://www.Pumptechnw.com

http://www.Pump-Zone.com

Two Steps to Longer Pump & Motor Life